A rhythm game series by Creator/{{Harmonix}} that doesn't depend on special peripherals. All that's needed is a PS2 controller. Each song has 6 main tracks (drums, guitar, etc.). On each track, there are a bunch of gems representing that track's instrument. Hitting all the gems on a track for two measures activates that track temporarily. Your job is to move around the tracks and hit all the gems to keep them all activated.

The first game was Frequency, followed by a sequel, Amplitude, both on the PS2.

After a successful Kickstarter campaign, a new [=HD=] Amplitude for the PS3 and PS4 with a new song list is in development and planned for release in 2015.

Made by Harmonix, who went on to make ''VideoGame/GuitarHero'' and ''VideoGame/RockBand''.

!!The game provides examples of:

* AndYourRewardIsClothes: the various "arenas" in which the songs can be played, and the actual clothes for your Freq in Amplitude
* CompetitiveMultiplayer: And one of the first games to use the PS2's online network adapter.
* DifficultButAwesome: There isn't much better moments of euphoria than beating any of Frequency's harder songs on Expert mode.
* DigitalAvatar: The Freqs.
* InterfaceScrew: some of the powerups in multiplayer.
* LuckBasedMission: Getting [[GameplayGrading four bars]] on many Amplitude songs is a ''lot'' easier if the Freestyler power-up appears in the right places.
** Not quite luck-based. The power-ups appear in the same location every time the song is played, requiring players to [[TrialAndErrorGameplay discover the optimal path]].
* NintendoHard: Given that the timing window is strictly hit-or-miss, the window for a hit is pretty small, especially in Frequency. If you're used to newer Harmonix games (or, worse yet, ''VideoGame/GuitarHero 3''+), or a newcomer to rhythm games, it can take some time to get used to. Compounded by the fact that [=TVs=] back then generally didn't have input lag...
* RankInflation: In Amplitude, your score at the end of a song is given a rating out of three bars, but the actual maximum you can get is four.
* RhythmGame
* {{Techno}}: The majority of the music library, though some songs dip into the trance and [[ThrashMetal thrash metal]] territory.